U.S. patent application number 12/202348 was filed with the patent office on 2009-11-19 for high performance optoelectronic device.
This patent application is currently assigned to TATUNG COMPANY. Invention is credited to Yi-Liang Chen, Chiung-Wei Lin.
Application Number | 20090283138 12/202348 |
Document ID | / |
Family ID | 41254083 |
Filed Date | 2009-11-19 |
United States Patent
Application |
20090283138 |
Kind Code |
A1 |
Lin; Chiung-Wei ; et
al. |
November 19, 2009 |
HIGH PERFORMANCE OPTOELECTRONIC DEVICE
Abstract
An optoelectronic device is provided. The optoelectronic device
includes a P-type semiconductor substrate, an N-type transparent
amorphous oxide semiconductor (TAOS) layer located on a surface of
the P-type semiconductor substrate, and a rear electrode on another
surface of the P-type semiconductor substrate. The N-type TAOS
layer constructs a portion of a P-N diode, and serves as a window
layer and a front electrode layer.
Inventors: |
Lin; Chiung-Wei; (Taipei,
TW) ; Chen; Yi-Liang; (Taipei, TW) |
Correspondence
Address: |
JIANQ CHYUN INTELLECTUAL PROPERTY OFFICE
7 FLOOR-1, NO. 100, ROOSEVELT ROAD, SECTION 2
TAIPEI
100
TW
|
Assignee: |
TATUNG COMPANY
Taipei
TW
TATUNG UNIVERSITY
Taipei
TW
|
Family ID: |
41254083 |
Appl. No.: |
12/202348 |
Filed: |
September 1, 2008 |
Current U.S.
Class: |
136/255 ;
257/E31.005 |
Current CPC
Class: |
H01L 31/0336 20130101;
H01L 31/072 20130101; H01L 31/109 20130101; Y02E 10/50 20130101;
H01L 31/0376 20130101; H01L 31/0328 20130101 |
Class at
Publication: |
136/255 ;
257/E31.005 |
International
Class: |
H01L 31/0336 20060101
H01L031/0336 |
Foreign Application Data
Date |
Code |
Application Number |
May 19, 2008 |
TW |
97118368 |
Claims
1. A diode, comprising: a P-type semiconductor substrate; and an
N-type transparent amorphous oxide semiconductor (TAOS) layer
disposed on the P-type semiconductor substrate.
2. The diode as claimed in claim 1, wherein the N-type transparent
amorphous oxide semiconductor layer is mainly formed by zinc oxide
(ZnO), a mixture of tin oxide and zinc oxide (a ZnO--SnO.sub.2
mixture), or a mixture of zinc oxide and indium oxide (a
ZnO--In.sub.2O.sub.3 mixture), and further comprises aluminum,
gallium, indium, boron, yttrium, scandium, fluorine, vanadium,
silicon, germanium, zirconium, hafnium, nitrogen, beryllium, or a
combination thereof.
3. The diode as claimed in claim 1, wherein the P-type
semiconductor substrate comprises a P-type silicon wafer, a P-type
silicon film, or other P-type semiconductor materials.
4. An optoelectronic device, comprising: a P-type semiconductor
substrate, comprising a first surface and a second surface; a rear
electrode disposed on the second surface of the P-type
semiconductor substrate; and an N-type transparent amorphous oxide
semiconductor layer disposed on the first surface of the P-type
semiconductor substrate, wherein the N-type transparent amorphous
oxide semiconductor layer and the P-type semiconductor substrate
construct a P--N diode.
5. The optoelectronic device as claimed in claim 4, wherein the
N-type transparent amorphous oxide semiconductor layer serves as a
window layer and a front electrode layer.
6. The optoelectronic device as claimed in claim 5, wherein the
N-type transparent amorphous oxide semiconductor layer is mainly
formed by ZnO, a ZnO--SnO.sub.2 mixture, or a ZnO--In.sub.2O.sub.3
mixture, and further comprises aluminum, gallium, indium, boron,
yttrium, scandium, fluorine, vanadium, silicon, germanium,
zirconium, hafnium, nitrogen, beryllium, or a combination
thereof.
7. The optoelectronic device as claimed in claim 5, wherein the
N-type transparent amorphous oxide semiconductor layer is formed by
a single conduction type material layer.
8. The optoelectronic device as claimed in claim 5, wherein the
N-type transparent amorphous oxide semiconductor layer consists of
two material layers having the same conduction types but with
different conductivities, and the material layer having lower
conductivity is close to the P-type semiconductor substrate.
9. The optoelectronic device as claimed in claim 5, wherein the
N-type transparent amorphous oxide semiconductor layer is formed by
a material layer having conductivity gradient, and a portion of the
material layer, which has lower conductivity, is close to the
P-type semiconductor substrate while another portion, which has
higher conductivity, is away from the P-type semiconductor
substrate.
10. The optoelectronic device as claimed in claim 4, further
comprising a front electrode layer formed by a metal, a transparent
conductive oxide, or a combination thereof, and disposed on the
transparent amorphous oxide semiconductor layer.
11. The optoelectronic device as claimed in claim 10, wherein the
metal comprises aluminum, silver, molybdenum, titanium, iron,
copper, silver, manganese, cobalt, nickel, gold, zinc, tin, indium,
chromium, platinum, tungsten, or an alloy thereof.
12. The optoelectronic device as claimed in claim 10, wherein the
transparent conductive oxide comprises indium tin oxide,
fluorin-doped tin oxide, aluminum-doped zinc oxide, gallium-doped
zinc oxide, or a combination thereof.
13. The optoelectronic device as claimed in claim 4, wherein the
P-type semiconductor substrate comprises a P-type silicon wafer, a
P-type silicon film, or other P-type semiconductor materials.
14. The optoelectronic device as claimed in claim 4, wherein the
optoelectronic device is a solar cell.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefit of Taiwan
application serial no. 97118368, filed on May 19, 2008. The
entirety of the above-mentioned patent application is hereby
incorporated by reference herein and made a part of
specification.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a diode adapted for an
optoelectronic device and a solar cell using the diode.
[0004] 2. Description of Related Art
[0005] A solar cell is capable of directly converting solar energy
into electricity. When it comes to pollutions and the shortage of
fossil fuel, the development of solar cells is brought into
focus.
[0006] A solar cell generates photo-electricity mainly through
photo-voltaic effect. Generally, a photo-voltaic effect refers to
an effect that two end electrodes of a P--N diode generate an
output voltage after photons are infused to the P--N diode to
generate current.
[0007] In a typical solar cell, an N-type-doped layer is formed on
a P-type silicon substrate by diffusion, and then a front electrode
and a rear electrode are formed at both sides of the P-type silicon
substrate. The front electrode is formed by metal, which inevitably
covers the N-type-doped layer underneath. As a consequence, the
amount of the photons incident to the N-type-doped layer is reduced
and the energy converting efficiency of the cell is seriously
affected. Further, a window layer that allows the entrance of
photons is usually disposed between the front electrode and the
N-type-doped layer to decrease the reflection of an incident light.
Such an arrangement not only complicates the fabricating process
but also increase the production costs thereof.
SUMMARY OF THE INVENTION
[0008] The present invention provides a new P--N diode
structure.
[0009] The present invention further provides an optoelectronic
device of a P--N diode, which is fabricated by a simple process to
reduce productions costs.
[0010] The present invention provides a diode adapted for an
optoelectronic device, which comprises a P-type semiconductor
substrate and an N-type transparent amorphous oxide semiconductor
(TAOS) layer.
[0011] According to an embodiment of the present invention, the
N-type transparent amorphous oxide semiconductor layer in the
aforesaid diode is mainly formed by zinc oxide (ZnO), a mixture of
tin oxide and zinc oxide (hereafter "a ZnO--SnO.sub.2 mixture"), or
a mixture of zinc oxide and indium oxide (hereafter "a
ZnO--In.sub.2O.sub.3 mixture"), and further comprises other
elements. The aforesaid other elements comprise aluminum, gallium,
indium, boron, yttrium, scandium, fluorine, vanadium, silicon,
germanium, zirconium, hafnium, nitrogen, beryllium, or a
combination thereof.
[0012] According to an embodiment of the present invention, the
P-type semiconductor substrate in the aforesaid diode comprises a
P-type silicon wafer, a P-type silicon film, or other P-type
semiconductor materials.
[0013] The present invention further provides an optoelectronic
device, which comprises a P-type semiconductor substrate, an N-type
transparent amorphous oxide semiconductor layer, and a rear
electrode. The N-type transparent amorphous oxide semiconductor
layer is disposed on a surface of the P-type semiconductor
substrate. The N-type transparent amorphous oxide semiconductor
layer and the P-type semiconductor substrate construct a P--N
diode. The rear electrode is disposed on another surface of the
P-type semiconductor substrate.
[0014] According to an embodiment of the present invention, the
N-type transparent amorphous oxide semiconductor layer in the
aforesaid optoelectronic device serves as a window layer and a
front electrode layer.
[0015] According to an embodiment of the present invention, the
N-type transparent amorphous oxide semiconductor layer in the
aforesaid optoelectronic device is mainly formed by ZnO, a
ZnO--SnO.sub.2 mixture, or a ZnO--In.sub.2O.sub.3 mixture, and
further comprises other elements. The aforesaid other elements
comprise aluminum, gallium, indium, boron, yttrium, scandium,
fluorine, vanadium, silicon, germanium, zirconium, hafnium,
nitrogen, beryllium, or a combination thereof. According to an
embodiment of the present invention, the N-type transparent
amorphous oxide semiconductor layer in the aforesaid optoelectronic
device is formed by a single conductive material layer.
[0016] According to an embodiment of the present invention, the
N-type transparent amorphous oxide semiconductor layer in the
aforesaid optoelectronic device consists of two material layers
having the same conduction types but with different conductivities,
wherein the material layer having lower conductivity is close to
the P-type semiconductor substrate.
[0017] According to an embodiment of the present invention, the
N-type transparent amorphous oxide semiconductor layer in the
aforesaid optoelectronic device is formed by a material layer
having conductivity gradient, wherein a portion of the material
layer, which has lower conductivity, is close to the P-type
semiconductor substrate while another portion, which has higher
conductivity, is away from the P-type semiconductor substrate.
[0018] According to an embodiment of the present invention, the
aforesaid optoelectronic device further comprises the front
electrode layer formed by a metal, a transparent conductive oxide,
or a combination thereof. The front electrode layer is disposed on
the transparent amorphous oxide semiconductor layer.
[0019] According to an embodiment of the present invention, the
metal for forming the front electrode layer comprises aluminum,
silver, molybdenum, titanium, iron, copper, silver, manganese,
cobalt, nickel, gold, zinc, tin, indium, chromium, platinum,
tungsten, or an alloy thereof.
[0020] According to an embodiment of the present invention, the
transparent conductive oxide for forming the front electrode layer
comprises indium tin oxide, fluorin-doped tin oxide, aluminum-doped
zinc oxide, gallium-doped zinc oxide, or a combination thereof.
[0021] According to an embodiment of the present invention, the
P-type semiconductor substrate in the aforesaid optoelectronic
device comprises a P-type silicon wafer, a P-type silicon film, or
other P-type semiconductor materials.
[0022] According to an embodiment of the present invention, the
optoelectronic device is a solar cell.
[0023] The P--N diode of the present invention is applicable in the
optoelectronic device.
[0024] The optoelectronic device of the present invention is
fabricated by a simpler process and requires less material, which
reduce production costs.
[0025] To make the above and other objectives, features, and
advantages of the present invention more comprehensible, preferable
embodiments accompanied with figures are detailed as follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
[0027] FIG. 1 is a schematic cross-sectional view of a diode
adapted for an optoelectronic device according to an embodiment of
the present invention.
[0028] FIG. 2 is a schematic cross-sectional view of a transparent
solar cell according to an embodiment of the present invention.
[0029] FIG. 3 is a schematic cross-sectional view of a transparent
solar cell according to another embodiment of the present
invention.
[0030] FIG. 4 is a schematic cross-sectional view of a transparent
solar cell according to yet another embodiment of the present
invention.
[0031] FIG. 5 is a schematic cross-sectional view of a transparent
solar cell according to yet another embodiment of the present
invention.
[0032] FIG. 6 illustrates the output characteristic curves of
current versus voltage by a diode according to an embodiment of the
present invention.
[0033] FIG. 7 illustrates the output characteristic curves of
current versus voltage by a solar cell according to an embodiment
of the present invention.
[0034] FIG. 8 is a diagram illustrating the relationship between
the reflectance versus wavelength, measured by a fluorescence
spectrophotometer, of a solar cell according to an embodiment of
the present invention and a P-type silicon wafer.
DESCRIPTION OF EMBODIMENTS
[0035] FIG. 1 is a schematic cross-sectional view of a diode
adapted for an optoelectronic device according to an embodiment of
the present invention.
[0036] Referring to FIG. 1, a diode 100 in this embodiment
comprises a P-type semiconductor substrate 10 and an N-type
transparent amorphous oxide semiconductor layer 12. The P-type
semiconductor substrate 10 can be a wafer or a film, for example, a
P-type silicon wafer or a P-type silicon film. The P-type
semiconductor substrate 10 can also be made of other P-type
semiconductor materials. The N-type transparent amorphous oxide
semiconductor layer 12 is disposed on the P-type semiconductor
substrate. The N-type transparent amorphous oxide semiconductor
layer 12 is, for example, mainly formed by ZnO, a ZnO--SnO.sub.2
mixture, or a ZnO--In.sub.2O.sub.3 mixture, and further comprises
other elements. The aforesaid other elements comprise aluminum,
gallium, indium, boron, yttrium, scandium, fluorine, vanadium,
silicon, germanium, zirconium, hafnium, nitrogen, beryllium, or a
combination thereof.
[0037] In this embodiment, the N-type transparent amorphous oxide
semiconductor layer 12 is formed by aluminum-doped zinc oxide
(ZnO:Al). The N-type transparent amorphous oxide semiconductor
layer 12 can be formed by physical vapor deposition (PVD), chemical
vapor deposition (CVD), a spin coating process, a sol-gel process,
or a sputtering process.
[0038] The aforesaid diode is applicable in an optoelectronic
device. In the following embodiment, a solar cell is taken as an
example to explain the applications of the diode.
[0039] FIG. 2 is a schematic cross-sectional view of a solar cell
according to an embodiment of the present invention.
[0040] Referring to FIG. 2, a solar cell 200 in this embodiment
consists of the P-type semiconductor substrate 10, a rear electrode
14, and the N-type transparent amorphous oxide semiconductor layer
12. The P-type semiconductor substrate 10 can be a wafer or a film
formed by a P-type semiconductor, for example, a P-type silicon
wafer or a P-type silicon film. The P-type semiconductor substrate
10 can also be formed by other P-type semiconductor materials. The
rear electrode 14 is disposed on a surface of the P-type
semiconductor substrate 10, and is formed by a metal, a transparent
conductive oxide (TCO), or a combination thereof. The metal is, for
example, aluminum, silver, molybdenum, titanium, iron, copper,
silver, manganese, cobalt, nickel, gold, zinc, tin, indium,
chromium, platinum, tungsten, or an alloy thereof. The transparent
conductive oxide is, for example, formed by indium tin oxide,
fluorin-doped tin oxide, aluminum-doped zinc oxide, gallium-doped
zinc oxide, or a combination thereof.
[0041] The N-type transparent amorphous oxide semiconductor layer
12 is disposed on another surface of the P-type semiconductor
substrate 10. In addition, the N-type transparent amorphous oxide
semiconductor layer 12 is, for example, mainly formed by ZnO, a
ZnO--SnO.sub.2 mixture, or a ZnO--In.sub.2O.sub.3 mixture, and
further comprises other elements. The aforesaid elements comprise
aluminum, gallium, indium, boron, yttrium, scandium, fluorine,
vanadium, silicon, germanium, zirconium, hafnium, nitrogen,
beryllium, or a combination thereof. In this embodiment, the N-type
transparent amorphous oxide semiconductor layer 12 is, for example,
formed by aluminum-doped zinc oxide (ZnO:Al).
[0042] In this embodiment, the N-type transparent amorphous oxide
semiconductor layer 12 and the P-type semiconductor substrate 10
construct a P--N diode, which serves as a photoelectric conversion
device. In addition, the N-type transparent amorphous oxide
semiconductor layer 12 also serves as a window layer to absorb
photons and a front electrode. Hence, the solar cell of this
embodiment does not require an additional window layer and an
additional front electrode. Consequently, light can be directly
incident to the N-type transparent amorphous oxide semiconductor
layer 12 without being blocked by the front electrode, to generate
current in a junction of the P-type semiconductor substrate 10.
[0043] Certainly, the present invention is not limited to the above
embodiment. Various modifications or alterations can be made to the
present invention. Other embodiments of the present invention are
detailed as follows.
[0044] FIG. 3 is a schematic cross-sectional view of a transparent
thin film solar cell according to another embodiment of the present
invention.
[0045] Referring to FIG. 3, a transparent thin film solar cell 300
in this embodiment consists of the P-type semiconductor substrate
10, the rear electrode 14, and an N-type transparent amorphous
oxide semiconductor layer 18. The material of the P-type
semiconductor substrate 10 and the arrangement and material of the
rear electrode 14 are the same as those in the above embodiment.
The descriptions thereof are therefore omitted herein. The N-type
transparent amorphous oxide semiconductor layer 18 is disposed on
another surface of the P-type semiconductor substrate 10. In
addition, the N-type transparent amorphous oxide semiconductor
layer 18, essentially formed by an N-type material, consists of two
transparent material layers 18a and 18b, which have different
conductivities. The material layer 18a, which has lower
conductivity, is closer to the P-type semiconductor substrate 10;
the material layer 18b, which has higher conductivity, is away from
the P-type semiconductor substrate 10.
[0046] In an embodiment, the components of the transparent material
layer 18a having lower conductivity is the same as that of the
transparent material layer 18b having higher conductivity, but the
proportions of the components are varied so as to have different
conductivities. The N-type transparent amorphous oxide
semiconductor layer 18 is, for example, mainly formed by ZnO, a
ZnO--SnO.sub.2 mixture, or a ZnO--In.sub.2O.sub.3 mixture, and
further comprises other elements. The aforesaid other elements
comprise aluminum, gallium, indium, boron, yttrium, scandium,
fluorine, vanadium, silicon, germanium, zirconium, hafnium,
nitrogen, beryllium, or a combination thereof. In an embodiment,
the material layer 18b of the N-type transparent amorphous oxide
semiconductor layer 18 is formed by aluminum-doped zinc oxide
(ZnO:Al) and the material layer 18a is also formed by
aluminum-doped zinc oxide (ZnO:Al), but the oxygen content of the
material layer 18b which has higher conductivity is lower. In
another embodiment, the composition of the material layer 18a
having lower conductivity is different from that of the material
layer 18b having higher conductivity. The material layer 18a which
has lower conductivity can be formed by ZnO, a ZnO--SnO.sub.2
mixture, a ZnO--In.sub.2O.sub.3 mixture, or a ZnO alloy such as
aluminum-doped zinc oxide (ZnO:Al). The material layer 18b which
has higher conductivity can be formed by ZnO, a ZnO--SnO.sub.2
mixture, a ZnO--In.sub.2O.sub.3 mixture, or a ZnO alloy such as
aluminum-doped zinc oxide (ZnO:Al). In an embodiment, the material
layer 18b of the N-type transparent amorphous oxide semiconductor
layer 18 is formed by aluminum-doped zinc oxide (ZnO:Al) while the
material layer 18a which has lower conductivity is formed by
non-aluminum-poded ZnO. In another embodiment, the material layer
18b of the N-type transparent amorphous oxide semiconductor layer
18 is formed by indium tin oxide, while the material layer 18a
which has lower conductivity is formed by aluminum-doped zinc oxide
(ZnO:Al).
[0047] In this embodiment, the material layer 18a having lower
conductivity in the N-type transparent amorphous oxide
semiconductor layer 18 and the P-type semiconductor substrate 10
construct a P--N diode, which serves as a photoelectric conversion
device. The material layer 18b having higher conductivity in the
N-type transparent amorphous oxide semiconductor layer 18 also
serves as a window layer to absorb photons and a front electrode.
Hence, the solar cell of this embodiment does not require an
additional window layer and an additional front electrode. As a
consequence, light can be directly incident to the N-type
transparent amorphous oxide semiconductor layer 18 without being
blocked by the front electrode, to generate current in a junction
of the P-type semiconductor substrate 10.
[0048] FIG. 4 is a schematic cross-sectional view of a solar cell
according to another embodiment of the present invention.
[0049] Referring to FIG. 4, a transparent thin film solar cell 400
of this embodiment comprises the P-type semiconductor substrate 10,
the rear electrode 14, and an N-type transparent amorphous oxide
semiconductor layer 20. The material of the P-type semiconductor
substrate 10 and the arrangement and material of the rear electrode
14 in this embodiment are similar to those in the embodiment of
FIG. 2. The descriptions thereof are therefore omitted herein. The
difference between this embodiment and the embodiment of FIG. 2
lies in the N-type transparent amorphous oxide semiconductor layer
20. Similarly, the N-type transparent amorphous oxide semiconductor
layer 20 is also disposed on another surface of the P-type
semiconductor substrate 10 and essentially formed by an N-type
material. However, the N-type transparent amorphous oxide
semiconductor layer 20 is formed by a material layer having
conductivity gradient distribute in the N-type transparent
amorphous oxide semiconductor layer 20. In the N-type transparent
amorphous oxide semiconductor layer 20, a portion closer to the
P-type semiconductor substrate 10 has lower conductivity; while
another portion which is away from the P-type semiconductor
substrate 10 has higher conductivity. During deposition, the
proportion of the composition of the N-type transparent amorphous
oxide semiconductor layer 20 can be varied to have conductivity
gradient in the N-type transparent amorphous oxide semiconductor
layer 20. The N-type transparent amorphous oxide semiconductor
layer 20 is, for example, mainly formed by ZnO, a ZnO--SnO.sub.2
mixture, or a ZnO--In.sub.2O.sub.3 mixture, and further comprises
other elements. The aforesaid other elements comprise aluminum,
gallium, indium, boron, yttrium, scandium, fluorine, vanadium,
silicon, germanium, zirconium, hafnium, nitrogen, beryllium, or a
combination thereof. In this embodiment, the N-type transparent
amorphous oxide semiconductor layer 20 is, for example, formed by
aluminum-doped zinc oxide (ZnO:Al), wherein the proportion of
oxygen atoms decreases from the portion near the P-type
semiconductor substrate 10 to the portion away from the P-type
semiconductor substrate 10.
[0050] In this embodiment, the portion having lower conductivity in
the N-type transparent amorphous oxide semiconductor layer 20 and
the P-type semiconductor substrate 10 construct a P--N diode, which
serves as a photoelectric conversion device. In the N-type
transparent amorphous oxide semiconductor layer 20, the portion
having higher conductivity simultaneously serves as a window layer
to absorb photons and a front electrode. Hence, the solar cell of
this embodiment does not require an additional window layer and an
additional front electrode. Consequently, light can be directly
incident to the N-type transparent amorphous oxide semiconductor
layer 20 without being blocked by the front electrode, to generate
current in a junction of the P-type semiconductor substrate 10.
[0051] FIG. 5 is a schematic cross-sectional view of a transparent
thin film solar cell according to yet another embodiment of the
present invention.
[0052] Referring to FIG. 5, if the shadowed area is not the
consideration, a front electrode 16 can be additionally formed on
the N-type transparent amorphous oxide semiconductor layer 12 in
the structure shown in FIG. 1. The front electrode 16 is, for
example, formed by a metal, a transparent conductive oxide, or a
combination thereof. The metal is, for example, aluminum, silver,
molybdenum, titanium, iron, copper, silver, manganese, cobalt,
nickel, gold, zinc, tin, indium, chromium, platinum, tungsten, or
an alloy thereof. The transparent conductive oxide is, for example,
formed by indium tin oxide, fluorin-doped tin oxide, aluminum-doped
zinc oxide, gallium-doped zinc oxide, or a combination thereof. In
other words, a transparent thin film solar cell 500 of this
embodiment, the N-type transparent amorphous oxide semiconductor
layer 12 is combined with the P-type semiconductor substrate 10 to
construct the P--N diode which is used as a photoelectric
conversion device, and meanwhile N-type transparent amorphous oxide
semiconductor layer 12 serves as a window layer to absorb photons.
The front electrode 16 and the rear electrode 14 can be formed by a
conventional metal or transparent conductive oxide.
[0053] In an embodiment, a P--N diode is constructed of an N-type
transparent amorphous oxide semiconductor layer formed by
aluminum-doped zinc oxide (ZnO:Al) and a P-type semiconductor
substrate formed by a P-type silicon wafer. Upon radiation
exposure, the output characteristic curves of the P--N diode are
illustrated in FIG. 6. Considering radiation exposure, the
characteristic curves of the current versus voltage output from a
solar cell formed by the aforesaid diode are illustrated in FIG. 7,
and the data is shown in Table 1.
TABLE-US-00001 TABLE 1 TAOS solar cell Results Work voltage V.sub.m
(Volt) 0.15 Maximum current I.sub.m (Ampere) 1.81 .times. 10.sup.-4
Open voltage V.sub.oc (Volt) 0.22 Short circuit current I.sub.sc
(Ampere) 2.94 .times. 10.sup.-4 Maximum output power P.sub.m (Watt)
2.71 .times. 10.sup.-5 Filling factor FF (%) 42.03 Conversion
efficiency .eta. (%) 0.34
[0054] Based on the measurement of the output current versus
voltage as shown in FIG. 7, a solar cell of aluminum-doped zinc
oxide has a favorable current-voltage (I-V) characteristic. It
proves that light can be effectively transmitted into the junction
of a P-type silicon wafer and a aluminum-doped zinc oxide film of
this type of aluminum-doped zinc oxide solar cell, so as to form an
internal electric field for effectively generating a photoelectric
current (FF=42.03%, V.sub.oc=0.22 V, J.sub.sc=2.94.times.10.sup.-4
A/cm.sup.2, .eta.=0.34%). Based on the above measurement results,
it is also known that the aluminum-doped zinc oxide film has the
characteristics of an N-type semiconductor layer, and the
aluminum-doped zinc oxide film can be directly deposited on the
P-type silicon wafer substrate to further simplify the fabrication
process of the solar cell. In addition, the opaque issue of
conventional semiconductor can be overcome by using the transparent
aluminum-doped zinc oxide film. Further, the top side of
aluminum-doped zinc oxide on the P-type silicon wafer structure is
not covered by any electrode, and therefore more visible light can
be effectively incident to the PN junction to generate more
current. The data in Table 1 shows that the P--N diode of the
present invention is also applicable in fabricating solar
cells.
[0055] The curves in FIG. 8 respectively illustrate the
relationship between the reflectance versus wavelength, measured by
a fluorescence spectrophotometer, of a P-type silicon wafer and an
N-type transparent amorphous oxide semiconductor layer of
aluminum-doped zinc oxide deposited on the P-type silicon wafer.
FIG. 8 shows that the reflectance in the range of short wavelength
is low, which indicates that the aluminum-doped zinc oxide film is
able to absorb short wavelength light; when compared with the
P-type silicon wafer, the aluminum-doped zinc oxide film also has
lower reflectance in the range of visible light. Hence, the
aluminum-doped zinc oxide film is able to absorb visible light as
well. The illustration of FIG. 8 proves that the reflectance is
lower within the wavelength range of 350 nm.about.1000 nm, which
means that aluminum-doped zinc oxide is capable of absorbing a
large portion of photons, and is therefore suitable to be used as a
photoelectric conversion device and a window layer.
[0056] The present invention applies the P--N diode formed by the
N-type transparent amorphous oxide semiconductor layer and P-type
silicon wafer to the optoelectronic device, so that the device can
have sufficient conversion efficiency. The N-type transparent
amorphous oxide semiconductor layer provides sufficient
conductivity. When applied to a solar cell, the N-type transparent
amorphous oxide semiconductor layer not only constructs a portion
of the P--N diode but also serves as a window layer to absorb
photons and a front electrode. As a consequence, it is not required
to additionally form a window layer and a front electrode. Hence,
the fabricating process is simplified, the material required is
reduced, and the production costs are decreased.
[0057] Although the present invention has been disclosed by the
above embodiments, the present invention is not limited thereto.
Persons skilled in the art may make some modifications and
alterations without departing from the spirit and scope of the
present invention. Hence, the protection range of the present
invention falls in the appended claims.
* * * * *